The present application relates to a wavelength selective optical switch platform, and in particular to a wavelength selective optical switch with a plurality of 1xc3x972 optical switches with independent channel equalization capabilities for use in a wavelength division multiplexing (WDM) configurable add/drop multiplexer (COADM) and/or dynamic gain equalizer (DGE).
In optical wavelength division multiplexed (WDM) communication systems, an optical waveguide simultaneously carries many different communication channels in light of different wavelengths. In WDM systems it is desirable to ensure that all channels have nearly equivalent power. To help achieve this, gain equalizers are disposed at various points throughout the system to control the relative power levels in respective channels.
Dense WDM systems require special add/drop multiplexers (ADM) to add and drop particular channels (i.e. wavelengths). For example, at predetermined nodes in the system, optical signals of predetermined wavelength are dropped from the optical waveguide and other signals of the same wavelength can then be added.
Typically, gain equalizing and add/drop multiplexer devices involve some form of multiplexing and demultiplexing to modify each individual channel of the telecommunication signal. In particular, it is common to provide a first diffraction grating for demultiplexing the optical signal and a second spatially separated diffraction grating for multiplexing the optical signal after it has been modified. An example of the latter is disclosed in U.S. Pat. No. 5,414,540, incorporated herein by reference. However, in such instances it is necessary to provide and accurately align two matching diffraction gratings and at least two matching lenses. This is a significant limitation of prior art devices.
To overcome this limitation, other prior art devices have opted to provide a single diffraction grating that is used to demultiplex an optical single in a first pass through the optics and multiplex the optical signal in a second pass through the optics. For example, U.S. Pat. Nos. 5,233,405, 5,526,155, 5,745,271, 5,936,752 and 5,960,133, which are incorporated herein by reference, disclose such devices.
However, none of these prior art devices disclose an optical arrangement suitable for both dynamic gain equalizer (DGE) and configurable optical add/drop multiplexer (COADM) applications. In particular, none of these prior art devices recognize the advantages of providing a simple, symmetrical optical arrangement suitable for use with various switching/attenuating means.
Moreover, none of the prior art devices disclose a multiplexing/demultiplexing optical arrangement that is compact and compatible with a plurality of parallel input/output optical waveguides.
For example, U.S. Pat. No. 5,414,540 to Patel et al. discloses a liquid crystal optical switch for switching an input optical signal to selected output channels. The switch includes a diffraction grating, a liquid crystal modulator, and a polarization dispersive element. In one embodiment, Patel et al. suggest extending the 1xc3x972 switch to a 2xc3x972 drop-add circuit and using a reflector. However, the disclosed device is limited in that the add/drop beams of light are angularly displaced relative to the input/output beams of light. This angular displacement is disadvantageous with respect to coupling the add/drop and/or input/output beams of light into parallel optical waveguides, in addition to the additional angular alignment required for the input beam of light.
With respect to compactness, prior art devices have been limited to an excessively long and linear configurations, wherein the input beam of light passes through each optical component sequentially before being reflected in a substantially backwards direction.
U.S. Pat. No. 6,081,331 discloses an optical device that uses a concave mirror for multiple reflections as an alternative to using two lenses or a double pass through one lens. However, the device disclosed therein only accommodates a single pass through the diffraction grating and does not realize the advantages of the instant invention.
An object of the present invention to provide an optical system including a diffraction grating that is relatively compact.
It is a further object of the instant invention to provide an optical configuration for rerouting and modifying an optical signal that can be used as a dynamic gain equalizer and/or configurable add/drop multiplexer.
Accordingly, the present invention relates to an optical device comprising:
a first port for launching an input beam of light including a plurality of wavelength channels;
a second port for receiving at least a portion of one of the plurality of wavelength channels;
first redirecting means for receiving the input beam of light, the first redirecting means having optical power;
a dispersive element for receiving the input beam of light from the first redirecting means, and for dispersing the input beam of light into the plurality of wavelength channels;
second redirecting means for receiving the dispersed wavelength channels, the second redirecting means having optical power; and
a plurality of modifying means, each modifying means for receiving one of the dispersed wavelength channels along one of a first series of paths, and for reflecting at least a portion each wavelength channel back along one of the first series of paths or back along one of a second series of paths;
wherein each of said modifying means includes first adjustable phase biasing means positioned in the first series of paths, and a second adjustable phase biasing means positioned in each of the second series of paths;
wherein wavelength channels traveling back along the first series of paths exit the first port via the second redirecting means, the dispersive element and the first redirecting means; and
wherein wavelength channels traveling back along the second series of paths exit the second port via the second redirecting means, the dispersive element and the first redirecting means.